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• SpringMvc java.lang.NullPointerException When Posting Form To Server

  - by dev_darin

  I have a form with a user name field on it when i tab out of the field i use a RESTFUL Web Service that makes a call to a handler method in the controller. The method makes a call to a DAO class that checks the database if the user name exists. This works fine, however when the form is posted to the server i call the same exact function i would call in the handler method however i get a java.lang.NullPointerException when it accesses the class that makes a call to the DAO object. So it does not even access the DAO object the second time. I have exception handlers around the calls in all my classes that makes calls. Any ideas as to whats happening here why i would get the java.lang.NullPointerException the second time the function is called.Does this have anything to do with Spring instantiating DAO classes using a Singleton method or something to that effect? What can be done to resolve this? This is what happens the First Time The Method is called using the Web Service(this is suppose to happen): 13011 [http-8084-2] INFO com.crimetrack.jdbc.JdbcOfficersDAO - Inside jdbcOfficersDAO 13031 [http-8084-2] DEBUG org.springframework.jdbc.core.JdbcTemplate - Executing prepared SQL query 13034 [http-8084-2] DEBUG org.springframework.jdbc.core.JdbcTemplate - Executing prepared SQL statement [SELECT userName FROM crimetrack.tblofficers WHERE userName = ?] 13071 [http-8084-2] DEBUG org.springframework.jdbc.datasource.DataSourceUtils - Fetching JDBC Connection from DataSource 13496 [http-8084-2] DEBUG org.springframework.jdbc.core.StatementCreatorUtils - Setting SQL statement parameter value: column index 1, parameter value [adminz], value class [java.lang.String], SQL type unknown 13534 [http-8084-2] DEBUG org.springframework.jdbc.datasource.DataSourceUtils - Returning JDBC Connection to DataSource 13537 [http-8084-2] INFO com.crimetrack.jdbc.JdbcOfficersDAO - No username was found in exception 13537 [http-8084-2] INFO com.crimetrack.service.ValidateUserNameManager - UserName :adminz does NOT exist The Second time When The Form Is 'Post' and a validation method handles the form and calls the same method the web service would call: 17199 [http-8084-2] INFO com.crimetrack.service.OfficerRegistrationValidation - UserName is not null so going to check if its valid for :adminz 17199 [http-8084-2] INFO com.crimetrack.service.OfficerRegistrationValidation - User Name in try.....catch block is adminz 17199 [http-8084-2] INFO com.crimetrack.service.ValidateUserNameManager - Inside Do UserNameExist about to validate with username : adminz 17199 [http-8084-2] INFO com.crimetrack.service.ValidateUserNameManager - UserName :adminz EXCEPTION OCCURED java.lang.NullPointerException

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• What would be a better implementation of shared variable among subclass

  - by Churk

  So currently I have a spring unit testing application. And it requires me to get a session cookie from a foreign authentication source. Problem what that is, this authentication process is fairly expensive and time consuming, and I am trying to create a structure where I am authenticate once, by any subclass, and any subsequent subclass is created, it will reuse this session cookie without hitting the authentication process again. My problem right now is, the static cookie is null each time another subclass is created. And I been reading that using static as a global variable is a bad idea, but I couldn't think of another way to do this because of Spring framework setting things during run time and how I would set the cookie so that all other classes can use it. Another piece of information. The variable is being use, but is change able during run time. It is not a single user being signed in and used across the board. But more like a Sub1 would call login, and we have a cookie. Then multiple test will be using that login until SubX will come in and say, I am using different credential, so I need to login as something else. And repeats. Here is a outline of my code: public class Parent implements InitializingBean { protected static String BASE_URL; public static Cookie cookie; ... All default InitializingBean methods ... afterPropertiesSet() { cookie = // login process returns a cookie } } public class Sub1 extends Parent { @resource public String baseURL; @PostConstruct public void init() { // set parents with my baseURL; BASE_URL = baseURL; } public void doSomething() { // Do something with cookie, because it should have been set by parent class } } public class Sub2 extends Parent { @resource public String baseURL; @PostConstruct public void init() { // set parents with my baseURL; BASE_URL = baseURL; } public void doSomethingElse() { // Do something with cookie, because it should have been set by parent class } }

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• Looking for an issue tracker / project management software that automatically manages start/completion dates based on priority/relationships

  - by user361910

  So, a little background. We are a small company with a half-dozen developers. We have been evaluating many project management / issue tracking software packages (TRAC, Redmine, FogBugz, etc) and trying to create a decent process/workflow for managing projects, adding features, fixing bugs, etc. I'd like to think our requirements are similar to most other companies our size. Essentially, what this comes down to is 1) An easy way for the PM and developers to track projects, issues, bugs, etc 2) An easy way for the PM and admin/executives to get a birds-eye view of progress and easily manage timelines, schedules, and priorities. After trying TRAC, we moved to Redmine. We found Redmine to be easier than track to administer and the ability to have sub-projects and sub-tickets is great. However, the big problem we ran into is the fact that it is very difficult to manage schedules and timelines. It seems like it would be incredibly time-intensive to manage because you have to manually enter a start date, estimated time, and end date for each ticket, project, etc. So if you setup a month's schedule based on priorities, what are you supposed to do when a particular ticket/issue/subproject takes up more time than was estimated. Right now, it appears I would have to go back in and MANUALLY change the start/end date of every single item. What would be ideal is to be able to set priorities/dependencies and estimated time on tickets/milestones, and have the software automatically manage the start/end dates. Does anyone know how to get Redmine to do this, or recommend a different software package that can do something like this!

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• issue with vhdl structural coding

  - by user3699982

  The code below is a simple vhdl structural architecture, however, the concurrent assignment to the signal, comb1, is upsetting the simulation with the outputs (tb_lfsr_out) and comb1 becoming undefined. Please, please help, thank you, Louise. library IEEE; use IEEE.STD_LOGIC_1164.all; entity testbench is end testbench; architecture behavioural of testbench is CONSTANT clock_frequency : REAL := 1.0e9; CONSTANT clock_period : REAL := (1.0/clock_frequency)/2.0; signal tb_master_clk, comb1: STD_LOGIC := '0'; signal tb_lfsr_out : std_logic_vector(2 DOWNTO 0) := "111"; component dff port ( q: out STD_LOGIC; d, clk: in STD_LOGIC ); end component; begin -- Clock/Start Conversion Generator tb_master_clk <= (NOT tb_master_clk) AFTER (1 SEC * clock_period); comb1 <= tb_lfsr_out(0) xor tb_lfsr_out(2); dff6: dff port map (tb_lfsr_out(2), tb_lfsr_out(1), tb_master_clk); dff7: dff port map (tb_lfsr_out(1), tb_lfsr_out(0), tb_master_clk); dff8: dff port map (tb_lfsr_out(0), comb1, tb_master_clk); end behavioural;

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• Sorted queue with dropping out elements

  - by ffriend

  I have a list of jobs and queue of workers waiting for these jobs. All the jobs are the same, but workers are different and sorted by their ability to perform the job. That is, first person can do this job best of all, second does it just a little bit worse and so on. Job is always assigned to the person with the highest skills from those who are free at that moment. When person is assigned a job, he drops out of the queue for some time. But when he is done, he gets back to his position. So, for example, at some moment in time worker queue looks like: [x, x, .83, x, .7, .63, .55, .54, .48, ...] where x's stand for missing workers and numbers show skill level of left workers. When there's a new job, it is assigned to 3rd worker as the one with highest skill of available workers. So next moment queue looks like: [x, x, x, x, .7, .63, .55, .54, .48, ...] Let's say, that at this moment worker #2 finishes his job and gets back to the list: [x, .91, x, x, .7, .63, .55, .54, .48, ...] I hope the process is completely clear now. My question is what algorithm and data structure to use to implement quick search and deletion of worker and insertion back to his position. For the moment the best approach I can see is to use Fibonacci heap that have amortized O(log n) for deleting minimal element (assigning job and deleting worker from queue) and O(1) for inserting him back, which is pretty good. But is there even better algorithm / data structure that possibly take into account the fact that elements are already sorted and only drop of the queue from time to time?

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• Getting Google repositories to work with apt-get on Ubuntu Hardy

  - by Justin

  I've installed Google Chrome on Hardy via the .deb file and would like to configure apt-get for automatic updates. [I have another machine running Ubuntu Karmic where this works fine; apt-get knows the package as 'google-chrome'; I'm now using a Dell Mini 10 with Ubuntu 8.04 LTS installed] As part of the .deb install, two entries have been added to the third- party software sources tab: http://dl.google.com/linux/deb stable main http://dl.google.com/linux/deb stable non-free main However if I check for updates with either of these clicked, I get the following error: Failed to fetch http://dl.google.com/linux/deb/dists/stable/Release Unable to find expected entry main/binary-lpia/Packages in Meta-index file (malformed Release file?) There is a thread here which indicates others have had the same problem: http://www.google.co.uk/support/forum/p/Chrome/thread?tid=097d103f87b49abe&hl=en This references a further thread: http://code.google.com/p/chromium/issues/detail?id=38608 which suggests the problem has been fixed. Despite this I remain unable to get it to work, and none of the suggested workarounds seem to work either. Ideas ? Thanks.

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• How to debug JBoss out of memory problem?

  - by user561733

  Hello, I am trying to debug a JBoss out of memory problem. When JBoss starts up and runs for a while, it seems to use memory as intended by the startup configuration. However, it seems that when some unknown user action is taken (or the log file grows to a certain size) using the sole web application JBoss is serving up, memory increases dramatically and JBoss freezes. When JBoss freezes, it is difficult to kill the process or do anything because of low memory. When the process is finally killed via a -9 argument and the server is restarted, the log file is very small and only contains outputs from the startup of the newly started process and not any information on why the memory increased so much. This is why it is so hard to debug: server.log does not have information from the killed process. The log is set to grow to 2 GB and the log file for the new process is only about 300 Kb though it grows properly during normal memory circumstances. This is information on the JBoss configuration: JBoss (MX MicroKernel) 4.0.3 JDK 1.6.0 update 22 PermSize=512m MaxPermSize=512m Xms=1024m Xmx=6144m This is basic info on the system: Operating system: CentOS Linux 5.5 Kernel and CPU: Linux 2.6.18-194.26.1.el5 on x86_64 Processor information: Intel(R) Xeon(R) CPU E5420 @ 2.50GHz, 8 cores This is good example information on the system during normal pre-freeze conditions a few minutes after the jboss service startup: Running processes: 183 CPU load averages: 0.16 (1 min) 0.06 (5 mins) 0.09 (15 mins) CPU usage: 0% user, 0% kernel, 1% IO, 99% idle Real memory: 17.38 GB total, 2.46 GB used Virtual memory: 19.59 GB total, 0 bytes used Local disk space: 113.37 GB total, 11.89 GB used When JBoss freezes, system information looks like this: Running processes: 225 CPU load averages: 4.66 (1 min) 1.84 (5 mins) 0.93 (15 mins) CPU usage: 0% user, 12% kernel, 73% IO, 15% idle Real memory: 17.38 GB total, 17.18 GB used Virtual memory: 19.59 GB total, 706.29 MB used Local disk space: 113.37 GB total, 11.89 GB used

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• Tools for managing code deployment/versioning for IIS / Windows enviroments

  - by RizwanK

  I've got a strong background in Linux and OSX, and just left a job where I was architecting systems based on those platforms. Now I've got a Windows Server running IIS that has a number of different websites that it hosts. Most of them are just a bunch of HTML, JS and Images, with some ASP for some customer tools. (Each website has a different set of customer tools, or they are the same tools, but with minor code changes between them.) I'm also adding a develop web server with the same code, but the 'bleeding edge' stuff. I need an effective way of managing changes and updates to the overall codebase (henceforth referring to both the images and the html and the asp, for all the sites). When a dev (or webmaster) checks in changes, I want it to show up automatically on the developer server, but should be manually pushed out to the live server. I'd be tempted to just make the websites SVN repositories, but I'd be concerned about the overhead of having the webdeveloper having to log into the server and trigger an SVN update via commandline/tortise (and heaven forbid, manage tags). Ideally I'd also manage IIS profile settings between the systems, but the major need is to be able to manage the process, and expose it to our ASP developer, and our webmaster, both of which are used to just FTPing up the files to the live site. So, any recommendations on tools (beyond some SVN hacking with BAT files + teaching the webmaster how to log into the server and do updates) or workflows that would help this out? I even considered an RPM type package (or some Windows equivalent, of course) to manage the live server, but that seems like a bit too much overhead. Thanks.

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• calling constructor of the class in the destructor of the same class

  - by dicaprio

  Experts !! I know this question is one of the lousy one , but still I dared to open my mind , hoping I would learn from all. I was trying some examples as part of my routine and did this horrible thing, I called the constructor of the class from destructor of the same class. I don't really know if this is ever required in real programming , I cant think of any real time scenarios where we really need to call functions/CTOR in our destructor. Usually , destructor is meant for cleaning up. If my understanding is correct, why the compiler doesn't complain ? Is this because it is valid for some good reasons ? If so what are they ? I tried on Sun Forte, g++ and VC++ compiler and none of them complain about it. using namespace std; class test{ public: test(){ cout<<"CTOR"<<endl; } ~test() {cout<<"DTOR"<<endl; test(); }};

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• Exemplars of large document-centric applications with COM/XPCOM/.NET interfaces.

  - by Warren P

  I am looking for exemplars (design examples) showing the use of interfaces (aka 'protocols' for you smalltalkers) to design a document management architecture in a large Word Processor, Spreadsheet, vector graphic or publishing package, or office-productivity (non-database) application with support for as many of the following as possible: any open source project, will be ideal, and language of implementation is unimportant since I am looking for design examples, however an object oriented language with support for "interfaces" is a must. I know at least a dozen languages, and I'm willing to study any application's source. use of "interface" could loosely be applied to either XPCOM or COM interfaces, or .NET interfaces, or even the use of pure-virtual (virtual+abstract) base-classes for OOP languages that lack the ability to declare an interface distinct from a class. I am mostly looking for a robust, thorough and flexible implementation for a document, IDocument, various document views (IDocumentView), and whatever operations make sense in that case. I am particular interested in cases where the product in question is a real-world product. For example, if anybody familiar with OpenOffice can tell me if the code contains a good sample design. I am looking for design documentation that outlines the design of the interfaces for such an application. So for example, if the openoffice spreadsheet has such an interface design, then that might be the best case, because it is a widely used real-world design, with millions of users, rather than a textbook example, which is minimal, and contrived. I know that the Mozilla platform uses XPCOM, and its design is heavily "interface" oriented, but I am looking more for a "word processor" or "spreadsheet" type of document design, rather than a web-browser. I am particularly interested in the interfaces used to access to data and meta-data such as markup (attributes like bold, and italics, and font size), and the ability to search and look up named entities within a document.

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• Stop Rewrite htaccess create random pages

  - by Vistol

  Recently I saw in my Webmaster tools that some random sites are linking to my site. Actually this is not an big issue. The issue comes when the pages that are linked are not real pages because of my httaccess file. This is the htaccess code that Im running: <pre> #Options +FollowSymLinks RewriteEngine on RewriteRule ^([^/\.]+)/?$ index.php?id=$1 [L] RewriteRule ^([0-9]+)/(.*)$ index.php?id=$1 [L] </pre> So the real URLs would be: mysite.com/folder/999/TITLE-OR-NAME But cecause I only check the 1st folder ($1) which is an I numberD, this htaccess file is allowing hackers linking to my site with random URLs like: mysite.com/folder/999/TITLE-OR-NAME1 mysite.com/folder/999/TITLE-OR-NAME2 mysite.com/folder/999/TITLE-OR-NAME3 mysite.com/folder/999/TITLE-OR-NAME4 mysite.com/folder/999/TITLE-OR-NAME5 The worst part comes when google tells me that I am duplicating content!!! Actually I am not duplicating content, the htaccess is duplicating it for me. And yes I know, Im a bad newbie programmer but Id really appreciate your help with this cause Im struggling to find a solution but it never. Thank you very much for all your support to this newbie :)

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• Consequent attribute calculations with a queuing system

  - by vrinek

  For all of the following assume these: rails v3.0 ruby v1.9 resque We have 3 models: Product belongs_to :sku, belongs_to :category Sku has_many :products, belongs_to :category Category has_many :products, has_many :skus When we update the product (let's say we disable it) we need to have some things happen to the relevant sku and category. The same is true for when a sku is updated. The proper way of achieving this is have an after_save on each model that triggers the other models' update events. example: products.each(&:disable!) # after_save triggers self.sku.products_updated # and self.category.products_updated (self is product) Now if we have 5000 products we are in for a treat. The same category might get updated hundreds of times and hog the database while doing so. We also have a nice queueing system, so the more realisting way of updating products would be products.each(&:queue_disable!) which would simply toss 5000 new tasks to the working queue. The problem of 5000 category updates still exists though. Is there a way to avoid all those updates on the db? How can we concatenate all the category.products_updated for each category in the queue?

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• How do i find if an object is before or after a waypoint?

  - by BoMann Andersen

  Im working on a racing game for a school project. Using Visual studio 10 pro, and Irrlicht. Sorry for bad grammar ., and its my first question so not sure if its done right. How i want it to work is that i make waypoints at different points on the track, and then i run my waypoint check to see if a car is past its next waypoint (the next it "needs" to go past), if yes then it updates the next waypoint, else nothing. The way i hope this will work is, i make a vector from n to n+1, then find the vector that is perpendicular to the first vector at n. Then i see if the object is in front or behind that vector. I found a Gamedev.net forumpost that helped me make this function: void Engine::checkWaypoint(Vehicle* vehicle) { btVector3 vector = waypoints[vehicle->nextWaypoint]; // n btVector3 nextVector = waypoints[vehicle->nextWaypoint + 1]; // n+1 vector = nextVector - vector; // First vector btVector3 pos = btVector3(vehicle->position.X,vehicle->position.Y,vehicle->position.Z); float product = vector.dot(pos - waypoints[vehicle->nextWaypoint]); // positiv = before, negative = behind if(product < 0) vehicle->nextWaypoint += 1; } Current bugs with this is: Updates the nextwaypoint more then ones without going past a new point. When it gets to the end and resets, it stops triggering on the first waypoints. So my questions: Is this an good way to do this? Did i do it right?

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• Choosing approach for an IM client-server app

  - by John

  Update: totally re-wrote this to be more succint. I'm looking at a new application, one part of which will be very similar to standard IM clients, i.e text chat, ability to send attachments, maybe some real-time interaction like a multi-user whiteboard. It will be client-server, i.e all traffic goes through my central server. That means if I want to support cross-communication with other IM systems, I am still free to pick any protocol for my own client<--server communication - my server can use XMPP or whatever to talk to other systems. Clients are expected to include desktop apps, but probably also browser-based as well either through Flex/Silverlight or HTML/AJAX. I see 3 options for my own client-server communication layer: XMPP. The benefits are clients already exist as do open-source servers. However it requires the most up-front research/learning and also appears like it might raise legal issues due to GPL. Custom sockets. A server app makes connections with the clients, allowing any text/binary data to be sent very fast. However this approach requires building said server from scratch, and also makes a JS client tricky Servlets (or similar web server). Using tried and tested Java web-stack, clients send HTTP requests similar to AJAX-based websites. The benefit is the server is easy to write using well-established technologies, and easy to talk to. But what restrictions would this bring? Is it appropriate technology for real-time communication? Advice and suggests are welcome, especially what pros and cons surround using a web-server approach as compared to a socket-based approach.

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• Flash browser game - HTTP + PHP vs Socket + Something else

  - by Maurycy Zarzycki

  I am developing a non-real time browser RPG game (think Kingdom of Loathing) which would be played from within a Flash app. At first I just wanted to make the communication with server using simply URLLoader to tell PHP what I am doing, and using $_SESSION to store data needed in-between request. I wonder if it wouldn't be better to base it on a socket connection, an app residing on a server written in Java or Python. The problem is I have never ever written such an app so I have no idea how much I'd have to "shift" my thoughts from simple responding do request (like PHP) to continuously working application. I won't hide I am also concerned about the memory and CPU usage of such Server app, when for example there would be hundreds of users connected. I've done some research. I have tried to do some research, but thanks to my nil knowledge on the sockets subject I haven't found anything helpful. So, considering the fact I don't need real time data exchange, will it be wise to develop the server side part as socket server, not in plain ol' PHP?

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• [PHP/MySQL] How to create text diff web app

  - by Adam Kiss

  Hello, idea I would like to create a little app for myself to store ideas (the thing is - I want it to do MY WAY) database I'm thinking going simple: id - unique id of revision in database text_id - identification number of text rev_id - number of revision flags - various purposes - expl. later title - self expl. desc - description text - self expl . flags - if I (i.e.) add flag rb;65, instead of storing whole text, I just said, that whenever I ask for latest revision, I go again in DB and check revision 65 Question: Is this setup the best? Is it better to store the diff, or whole text (i know, place is cheap...)? Does that revision flag make sense (wouldn't it be better to just copy text - more disk space, but less db and php processing. php I'm thinking, that I'll go with PEAR here. Although main point is to open-edit-save, possiblity to view revisions can't be that hard to program and can be life-saver in certain situations (good ideas got deleted, saving wrong version, etc...). However, I've never used PEAR in a long-time or full-project relationship, however, brief encounters in my previous experience left rather bad feeling - as I remember, it was too difficult to implement, slow and humongous to play with, so I don't know, if there's anything better. why? Although there are bazillions of various time/project/idea management tools, everything lacks something for me, whether it's sharing with users, syncing on more PCs, time-tracking, project management... And I believe, that this text diff webapp will be for internal use with various different tools later. So if you know any good and nice-UI-having project management app with support for text-heavy usage, just let me know, so I'll save my time for something better than redesigning the weel.

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• how to create a https proxy?

  - by davidshen84

  hi, i want to implement a simple ssl web proxy. i do not want to work with the network connection problems. so i think i can utilize a web server (like apache) to help me establish the connection, and my program works like a cgi app on the web server to redirect the web browser request. below is how i want to implement it: client make http/https requests to the target web site, and setting to use my http/https proxy; apache get the request, and use a rewrite rule to redirect the to my cgi app; my app parse the request and make request to the real web site; my app get the response from the real web site, then send the response back to the client; currently, http requests seem to work. but https requests do not work at all. i tried to use curl to make a request to a https web site through my proxy, and the result is CONNECTION FAILED. my question is, will my idea work? if yes, how to make the https requests work.

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• Visual C++ function suddenly 170 ms slower (4x longer)

  - by Mikael

  For the past few months I've been working on a Visual C++ project to take images from cameras and process them. Up until today this has taken about 65 ms to update the data but now it has suddenly increased significantly. What happens is: I launch my program and for the first 30 or so iterations it performs as expected, then suddenly the loop time increases from 65 ms to 250 ms. The odd thing is, after timing each function I found out that the part of the code which is causing the slowdown is fairly basic and has not been modified in over a month. The data which goes into it is unchanged and identical every iteration but the execution time which is initially less than 1 ms suddenly increases to 170 ms while the rest of the code is still performing as expected (time-wise). Basically, I am calling the same function over and over, for the first 30 calls it performs as it should, after that it slows down for no apparent reason. It might also be worth noting that it is a sudden change in execution time, not a gradual increase. What could be causing this? The code is leaking some memory (~50 kb/s) but not nearly enough to warrant a sudden 4x slowdown. If anyone has any ideas I'd love to hear them!

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• MS 70-536 .NET Framework Foundation - info on Exam? Especially regex?

  - by Sebastian P.R. Gingter

  Hi, I know there are already some questions about this, but not that specific. I have the self-paced training kit and worked through the test exam tool that is on the CD coming with the book. I constantly fail on the test tool, mostly on the regex questions. I'm not a regex guru. In fact my regex-fu is more than weak. I know what regex'es are, how I can use them and where my 'Regular expressions - kurz und gut' book is in my drawer in case I really need them. And to be honest I feel like learning regex is a total waste of time, because if I need them I have either a colleague that is fit and can do them in just a few seconds or I need my book and get them right in a still fair amount of time. And from my experience I can tell that I need regex like once in two or three years. So just putting in a lot of time into learning just the expressions to pass the exam is.. something I like not to have to do. Can you tell me something about the real exam vs. the test exam tool on the book and about the need to know regex for passing it? Thank you for your time. Marked as Community Wiki. Hope that fits?

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• custom sorting or ordering a table without resorting the whole shebang

  - by fuugus

  for ten years we've been using the same custom sorting on our tables, i'm wondering if there is another solution which involves fewer updates, especially since today we'd like to have a replication/publication date and would'nt like to have our replication replicate unnecessary entries. i had a look into nested sets, but it does'nt seem to do the job for us. base table: id | a_sort ---+------- 1 10 2 20 3 30 after inserting insert into table (a_sort) values(15) an entry at the second position. id | a_sort ---+------- 1 10 2 20 3 30 4 15 ordering the table with select * from table order by a_sort and resorting all the a_sort entries, updating at least id=(2,3,4) will of course produce the desired output id | a_sort ---+------- 1 10 4 20 2 30 3 40 the column names, the column count, datatypes, a possible join, possible triggers or the way the resorting is done is/are irrelevant to the problem. also we've found some pretty neat ways to do this task fast. only; how the heck can we reduce the updates in the db to 1 or 2 max. seems like an awfully common problem. the captain obvious in me thougth once "use an a_sort float(53), insert using a fixed value of ordervaluefirstentry+abs(ordervaluefirstentry-ordervaluenextentry)/2".. but this would only allow around 1040 "in between" entries - so never resorting seems a bit problematic ;)

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• Is there an efficient algorithm to distribute resources in a way that both avoids conflict and allows bias?

  - by Steve V.

  Background (Skip this if you only care about the algorithm) At the university where I work, one of the biggest hassles in our department is classroom scheduling. For illustration purposes and to lay out the scope of the problem, here's how we do scheduling now: Professors give us a list of the classes they're teaching with the time slots they'd prefer to teach, ranked in order of priority (most desired to least desired). Administration gives us a list of the rooms we may assign along with the times those rooms are available for our department's use. We start assigning professors to rooms trying (at first) to take into account the preferences of the various professors. Inevitably, conflicts arise, professors start asking for changes, and the plan falls to pieces somewhere around professor number 30, at which point we start assigning rooms basically wherever we can fit them in, crumpled pieces of paper are everywhere, and nobody's happy. (If you've ever wondered why your class was at 9.30 in the morning on Thursday but 4 pm every other day, now you know) I have been asked to quietly investigate whether software could do this more optimally. The Actual Question Is there an algorithm to efficiently schedule a set of resources such that the following criteria are met: The algorithm must never assign two professors to the same room at the same time. The task is not complete until every professor has been assigned a room / time. The algorithm need not worry about having too many professors for the amount of time slots available. (We're not that well funded.) As much as is possible the algorithm should respect the scheduling preferences of the individual professors. I feel like I can't be the first one to ask this. Is there a efficient algorithm for this, or is this the sort of problem that can only be brute-forced?

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• Is there any better way to capture the screen than PIL.ImageGrab.grab()?

  - by user1474837

  I am making a screen capture program with python. My current problem is PIL.ImageGrab.grab() gives me the same output as 2 seconds later. For instance, for I think I am not being clear, in the following program, almost all the images are the same, have the same Image.tostring() value, even though I was moving my screen during the time the PIL.ImageGrab.grab loop was executing. >>> from PIL.ImageGrab import grab >>> l = [] >>> import time >>> for a in l: l.append(grab()) time.sleep(0.01) >>> for a in range(0, 30): l.append(grab()) time.sleep(0.01) >>> b = [] >>> for a in l: b.append(a.tostring()) >>> len(b) 30 >>> del l >>> last = [] >>> a = 0 >>> a = -1 >>> last = "" >>> same = -1 >>> for pic in b: if b == last: same = same + 1 last = b >>> same 28 >>> This is a problem, as all the images are the same but 1. 1 out of 30 is different. That would make for a absolutly horrable quality video. Please, tell me if there is any better quality alternative to PIL.ImageGrab.grab(). I need to capture the whole screen. Thanks!

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• Are reads and (transactional) writes faster for entities of the same group than otherwise?

  - by indiehacker

  What advantage is there to designing child-parent relationships, which allow us to do writes in transactions, when there is never a real concern for consistency and contention and those sort of more complex issues? Does it make writes and reads faster? Consider my situation where there are many .png images that are referenced to one mosaic layer, and these .png images are written just once by a single user. The user can design many mosaic layers and her mosaic layers and referenced image entities are never changed/updated, they are just deleted some time in the future. Other users can come to the web project site and interactively view the mosaic layer as different layouts/configurations of the images as they play (query) with different criteria. So reads should be very fast. So there is no real worry of contention, or users conflicting with one another with writing new image entities. And because of that I am assuming there is no "requirement" for the .png image entities to be grouped by their same mosaic layer in child-parent relationship. However, perhaps, since the documentation says they are stored close to one another, if the many image entities were grouped as children to a single mosaic layer parent than this has the advantage that the writing (in transaction) and reading will happen much faster?

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• Save a tab in a jQuery Modal Window for future Display

  - by Shauni

  Hello, long time reader, first time poster. I’m coming with an issue that many of you will find trivial but I’m bashing my head against it for too long time and I can’t seems to find any clue on the internet. As a total scrubs with JavaScript, I’m trying to use JQuery.ui smartmodal windows (v 1.8.rc1) for displaying two football teams in two separate tabs. Like France in Tab(0) and England in Tab(1). When I open this modal window, the first tab (France) is always opened by default. Everything’s fine until here : I’m trying to improve this modal window by remembering what was the last Tab the user was looking when he closed the modal, for reopening it (in spite of the first tab, by default) when the user will reopen this modal latter on. I’ve already tried to use the “selecting & loading a jquery tab programatically » method but without any kind of success, and I’m slowly running out of options (and time). Thanks for reading me, if you have any idea on how can I use a parameter in the smartmodal call, that would greatly help me.

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• wxpython - Running threads sequentially without blocking GUI

  - by ryantmer

  I've got a GUI script with all my wxPython code in it, and a separate testSequences module that has a bunch of tasks that I run based on input from the GUI. The tasks take a long time to complete (from 20 seconds to 3 minutes), so I want to thread them, otherwise the GUI locks up while they're running. I also need them to run one after another, since they all use the same hardware. (My rationale behind threading is simply to prevent the GUI from locking up.) I'd like to have a "Running" message (with varying number of periods after it, i.e. "Running", "Running.", "Running..", etc.) so the user knows that progress is occurring, even though it isn't visible. I'd like this script to run the test sequences in separate threads, but sequentially, so that the second thread won't be created and run until the first is complete. Since this is kind of the opposite of the purpose of threads, I can't really find any information on how to do this... Any help would be greatly appreciated. Thanks in advance! gui.py import testSequences from threading import Thread #wxPython code for setting everything up here... for j in range(5): testThread = Thread(target=testSequences.test1) testThread.start() while testThread.isAlive(): #wait until the previous thread is complete time.sleep(0.5) i = (i+1) % 4 self.status.SetStatusText("Running"+'.'*i) testSequences.py import time def test1(): for i in range(10): print i time.sleep(1) (Obviously this isn't the actual test code, but the idea is the same.)

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